1. Field of the Invention
The present invention relates to a base station (specifically, a femto base station) and a mobile communication method.
2. Description of the Related Art
There has recently been developed a base station that can be installed as needed by a user. The base station is called a “femto base station” since a radius of a cell under the control thereof is smaller than that of a “macro base station” which is installed, designed and operated by a carrier.
An installation location of the femto base station may be outside the management of the carrier. Thus, the femto base station has been expected to have a cell radius autonomous adjustment function for increasing or reducing the radius of a cell under the control thereof so as to cover a desired communication area. Specifically, this function can reduce the cell radius so that the femto base station may not interfere with the existing macro base station, or reversely, can increase the cell radius so that the femto base station can overcome interference from the existing macro base station.
Here, when the femto base station reduces the radius of the cell under the control thereof, there may occur a situation where a macro mobile station which is not registered with the femto base station communicates with the macro base station without communicating with the femto base station although the macro mobile station is adjacent to the femto base station.
In such a case, since the macro base station is more distant from the macro mobile station than the femto base station, the macro mobile station performs uplink transmission with a large amount of power, which causes significant interference to the femto base station adjacent to the macro mobile station. Thus, there is a problem that the quality of unlink communication between a femto mobile station and the femto base station may deteriorate, or that the femto mobile station and the femto base station may no longer be able to communicate with each other.
Specifically, the conventional femto base station can change a radius of a downlink femto cell by changing a transmission power of a perch channel signal according to interference with a neighboring base station (macro base station), traffic congestion or service needs. However, when only the size of the downlink femto cell is changed, there may be a problem of deterioration of the uplink communication quality.